VALID FOR TUESDAY EVENING/NIGHT (OCTOBER 14, 2014) SPC AC 131730 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1230 PM CDT MON OCT 13 2014 VALID 141200Z - 151200Z ...THERE IS A SLGT RISK OF SVR TSTMS TUES INTO TUES NIGHT ACROSS PORTIONS OF THE LOWER OHIO VALLEY INTO THE CENTRAL AND SOUTHERN APPALACHIANS...AND ACROSS THE EASTERN GULF INTO SOUTH ATLANTIC COAST STATES... ...SUMMARY... THE RISK FOR POTENTIALLY DAMAGING WIND GUSTS AND A FEW TORNADOES IS EXPECTED TO ACCOMPANY THUNDERSTORM ACTIVITY TUESDAY INTO TUESDAY NIGHT ACROSS PARTS OF THE LOWER OHIO VALLEY INTO CENTRAL AND SOUTHERN APPALACHIANS...AS WELL AS ACROSS THE EASTERN GULF COAST INTO THE SOUTH ATLANTIC COAST. ...SYNOPSIS... THE MID/UPPER CLOSED LOW...NOW OVER THE SOUTHERN PLAINS...APPEARS LIKELY TO DEVELOP NORTHEASTWARD INTO THE MIDDLE MISSISSIPPI VALLEY...BEFORE GENERALLY BECOMING CUT-OFF FROM THE STRONGER WESTERLIES. HOWEVER...A SLOW EASTWARD PROGRESSION OF THE CYCLONIC CIRCULATION...AND UPPER TROUGHING TRAILING TO THE SOUTH...IS FORECAST TUESDAY THROUGH TUESDAY NIGHT...AS A SIGNIFICANT UPSTREAM TROUGH WITHIN THE WESTERLIES PROGRESSES INTO THE PACIFIC COAST. MODELS DO INDICATE SUBSTANTIAL WEAKENING OF THE ASSOCIATED SURFACE CYCLONE ACROSS THE MIDDLE MISSISSIPPI INTO LOWER OHIO VALLEYS DURING THIS PERIOD. HOWEVER...LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION...IN THE PRESENCE OF SUFFICIENTLY MOIST CONDITIONS TO SUPPORT WEAK TO MODEST CONDITIONAL INSTABILITY...IS EXPECTED TO SUPPORT CONSIDERABLE CONVECTION...INCLUDING THUNDERSTORM ACTIVITY...ACROSS THE GREAT LAKES...OHIO VALLEY AND SOUTHEASTERN STATES. AND WEAKENING OF LOWER/MID TROPOSPHERIC WIND FIELDS MAY BE SLOW ENOUGH TO MAINTAIN A RISK FOR SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER OHIO VALLEY INTO CENTRAL AND SOUTHERN APPALACHIANS...AS WELL AS ACROSS PARTS OF THE EASTERN GULF STATES INTO THE SOUTH ATLANTIC COAST. ...OHIO VALLEY INTO APPALACHIANS AND SOUTHEAST... BY 12Z TUESDAY...MODELS GENERALLY SUGGEST THAT A PRE-COLD FRONTAL 50-70 KT SOUTHERLY 850 MB JET CORE WILL EXTEND FROM THE UPPER TENNESSEE VALLEY NORTHWARD ACROSS THE LOWER OHIO VALLEY...TOWARD THE GREAT LAKES REGION. WHILE WEAKENING OF THIS FEATURE IS FORECAST THROUGH THE PERIOD AS IT SHIFTS EASTWARD ACROSS THE APPALACHIANS AND LOWER GREAT LAKES REGION...IT APPEARS THAT THIS MAY BE SLOW...AT LEAST DURING THE DAYTIME HOURS...WHEN BOUNDARY LAYER DESTABILIZATION MAY BECOME JUXTAPOSED WITH STRONG TO EXTREME LOW-LEVEL SHEAR. ALTHOUGH THIS INSTABILITY PROBABLY WILL BE LIMITED DUE TO WEAK LOWER/MID TROPOSPHERIC LAPSE RATES...A BAND OF FRONTAL FORCING OVERSPREADING CENTRAL AND EASTERN KENTUCKY AND TENNESSEE DURING THE DAY PROBABLY WILL BE SUFFICIENT TO SUPPORT THUNDERSTORM ACTIVITY. GIVEN THIS DEVELOPMENT...AND THE SIZE OF THE FORECAST LOW-LEVEL HODOGRAPHS...STRONGEST STORMS WILL BE ACCOMPANIED BY THE RISK FOR POTENTIALLY DAMAGING WIND GUSTS AND TORNADOES...AND COULD REACH THE WESTERN SLOPES OF THE APPALACHIANS BEFORE WEAKENING TUESDAY EVENING. FARTHER SOUTH...ACROSS THE EASTERN GULF STATES...SOUTHERLY DEEP LAYER MEAN FLOW FIELDS AND SHEAR WILL BE WEAKER /30-50 KT/...BUT STILL SUFFICIENTLY STRONG FOR ORGANIZED CONVECTIVE DEVELOPMENT IN THE PRESENCE OF MIXED LAYER CAPE ON THE ORDER OF 500-1000 J/KG BY TUESDAY AFTERNOON. ALTHOUGH FORCING FOR UPWARD VERTICAL MOTION APPEARS LIKELY TO BE WEAKER...OR LESS FOCUSED...BROKEN BANDS OR CLUSTERS OF STORMS APPEAR POSSIBLE WITHIN BROADLY CONFLUENT LOW-LEVEL FLOW. THIS MAY INCLUDE DISCRETE SUPERCELL DEVELOPMENT...WITH THE RISK FOR A COUPLE OF TORNADOES...IN ADDITION TO LOCALLY DAMAGING WIND GUSTS. ..KERR.. 10/13/2014
Posted on: Tue, 14 Oct 2014 03:12:29 +0000
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